Hmm.. I can't find any pics, but shorten the Chimera top plate and move it back so you can mount the turret towards the rear. There will be some gaps that you'll need to cover.
Then bulk up the turret or create your own plasticard one, load it with autocannons, and you're good to go.

Also it's more costly, but you could order an Aegis defence line and use the quad autocannon turret. That's what I plan to do for my Mechanicus Hydra battery

There is no such thing as a plea for innocence in my court. A plea for innocence is guilty of wasting my time. Guilty.
- Inquisitor Lord Fyodor Karamazov

Hmm.. I can't find any pics, but shorten the Chimera top plate and move it back so you can mount the turret towards the rear. There will be some gaps that you'll need to cover.
Then bulk up the turret or create your own plasticard one, load it with autocannons, and you're good to go.

Also it's more costly, but you could order an Aegis defence line and use the quad autocannon turret. That's what I plan to do for my Mechanicus Hydra battery

I'd go with the aegis defense line, and plasticard.
When you make your chimera either:
don't put on the top plate, or
make the hatch removeable (with the hydra guns slotting on top where they were.
You could look at the forgeworld one for the design of how it should go.

there's lots of ways to do it, from using reg. AC to making your own. The top of a rhino (razorback roof) fits perfectly longways meaning you could easily stack one ontop of a razorback or predator mount. The thing I found out is, that in July, they'll be releasing their Planetstrike stuff, and some of it's terrain/buildings comes with the quad AC mount exactly like the mold from ForgeWorld, so if you can wait a month, you should have as many as you want.

I'd go with the aegis defense line, and plasticard.
When you make your chimera either:
don't put on the top plate, or
make the hatch removeable (with the hydra guns slotting on top where they were.
You could look at the forgeworld one for the design of how it should go.

The Aegis Defense Line is an awesome deal

There is going to be a combo deal, 3 Defense Lines and 2 Towers for ~$90